For over 30 years the F-14 formed the backbone of the US Navy air defence system and is one of the most advanced carrier-borne weapons platforms. The F-14D was developed from the modernization programme of the F-14A, the capabilities of which had proved inadequate. The decision had already been taken in 1973 to equip an F-14 with different engines. The experience gained finally gave rise to the F-14D with the GE F-110-GE-400 engine, upgraded electronics, a new on-board radar system and modified aerodynamics. Production of the Grumman F-14D began in March 1990. On 10th March 2006 the aircraft from the last two Tomcat squadrons (VF-31 and VF-213) returned from their last mission to NAS Oceana. All 22 Tomcats overflew the site in a crescent formation to the applause of hundreds of spectators. The official "Tomcat Sunset" decommissioning ceremony took place on 22nd September 2006 in Oceana. VF-31 was the last active squadron.